Cadmium

Reaction of cadmium with acetic acid

Reaction of cadmium with air

Under normal pressure and temperature, Cd does not react with the air. Polished Cd is matted after a while, forming CdO [5].

At 300 °C Cd forms a thin brown gas-permeable coating. The yield increases parabolic with temperature [5].

Cadmium metal burns in air to form cadmium(II)oxide. The burning temperature is above the sublimations temperature of CdO, 1385 °C [5].

2 Cd(s) + O₂(g) 2 CdO(s)

Reaction of cadmium with ammonia

Cd does not react with NH₃ in its gaseous form until 255 °C. Above 255 °C is unknown. In aqueous solution NH₃ dissolves Cd. Cd²⁺ forms complexes with NH₃(aq). The average number of NH₃ per Cd is four but varies depending on [Cd²⁺] and [NH₃] [5].

Cd(s) + NH₃(g)
Cd(s) + 4 NH₃(aq) Cd²⁺(aq) + ??
Cd²⁺(aq) + 4 NH₃(aq) [Cd(NH₃)₄]²⁺(aq)

Reaction of cadmium with arsenic

Gaseous arsenic reacts with solid Cd forming Cd₃As₂ at around 700 °C [5].

3 Cd(s) + 2 As(g) Cd₃As₂(s)

Reaction of cadmium with halogens

Cd(s) + F₂(g) CdF₂(s) [white]

Cd reacts directly with Cl₂ in aqueous solution [5].

Cd(s) + Cl₂(aq) Cd²⁺(aq) + 2 Cl⁻(aq)


Cd reacts directly with Br₂ in aqueous solution and Br₂(g) at 450 °C [5].

Cd(s) + Br₂(aq) Cd²⁺(aq) + 2 Br⁻(aq)
Cd(s) + Br₂(g) CdBr₂(s) [pale yellow]


Solid Cd does not react with I₂(g), but will react with I₂(aq). In gas phase Cd and I₂ will react forming CdI₂. At high temperature and pressure (e.g. a steel bomb) equivalent Cd and I₂ will react forming CdI [5].

Cd(s) + I₂(aq) Cd²⁺(aq) + 2 I⁻(aq)
Cd(g) + I₂(g) CdI₂(g)
2 Cd(g) + I₂(g) 2CdI(g)

Reaction of cadmium with hydroxide

Metallic cadmium does not dissolve in aqueous alkalis such as potassium hydroxide, KOH. Cd²⁺ is precipitated by excess amounts of OH⁻ at pH > 7.5 [5]

Cd(s) + OH⁻(aq)
Cd²⁺(aq) + 2 OH⁻(aq) Cd(OH)₂(s)

Reaction of cadmium with hydrobromic acid

Cd reacts with hydrobromic acid forming CdBr₂ [5].

Cd(s) + 2 HBr(aq) CdBr₂(s) + H₂(g)

Reaction of cadmium with hydrochloric acid

Cd reacts with hydrochloric acid forming CdCl₂ [5].

Cd(s) + 2 HCl(aq) CdCl₂(s) + H₂(g)

Reaction of cadmium with hydrofluoric acid

Cd reacts with hydrofluoric acid forming CdF₂ [5].

Cd(s) + 2 HF(aq) CdF₂(s) + H₂(g)

Reaction of cadmium with hydrogen

Cd usually does not react with H₂(g). At 450°C H₂ is adsorbed in the metal. When the metal has reached max. adsorption the temperature will increase and Cd reacts with H₂ [5].

Cd(s) + H₂(g) CdH(s) + H·

Reaction of cadmium with hypochlorite

Cd reacts with hypochlorite forming Cd(ClO₂)₂ and after a while also Cd(ClO₃)₂ [5].

Cd(s) + 2 HClO₂(aq) Cd(ClO₂)₂(s) + H₂(g) Cd(ClO₃)₂(s)

Reaction of cadmium with nitric acid

Cd does not react with the fumes from concentrated nitric acid [5].

Cd(s) + HNO₃(g)

Dilute hot nitric acid will dissolve Cd, forming nitrogen monooxide

3 Cd(s) + 2 NO₃-(aq) + 8 H⁺(aq) Cd²⁺(aq) + 2 NO(g) + H₂O(l)

Reaction of cadmium with phosphorus

Cd reacts with P at elevated temperatures in an exoterm process forming Cd₃P₂ and CdP₂ [5].

4 Cd(s) + P₄(s) Cd₃P₂(s) + CdP₂(s)

Reaction of cadmium with ortho- and pyrophosphoric acid

Cd²⁺ is precipitated by ortho- and pyrophosphoric acid in an acetic acid/acetate-buffer [5].

3 Cd²⁺(aq) + 2 PO₄³⁻(aq) Cd₃(PO₄)₂(s)
3 Cd²⁺(aq) + P₂O₇⁴⁻(aq) + H₂O(l) Cd₃(PO₄)₂(s) + 2 H⁺(aq)

Reaction of cadmium with selenium and selenium compounds

Cd reacts with Se when heated rigorously [5].

Cd(s) + Se(s) CdSe(s)


Cd reacts with H₂Se forming CdSe [5].

Cd(s) + H₂Se(s) CdSe(s) + H₂(g)


Cd reacts with Se₂Cl₂ forming CdSe. The reaction is slow and requires heat [5].

Cd(s) + Se₂Cl₂(s) CdSe(s)

Reaction of cadmium with sulfides

In dry air Cd reacts very slowly with H₂S forming CdS. The reaction increases with increasing moisture in the air [5].

Cd(s) + H₂S(g) CdS(s) [yellow]

In strong acids like HCl and H₂SO₄, Cd²⁺ is precipitated by H₂S as CdS. It should be noted that the precipitate is not pure but a mixture of CdS-CdCl₂ or CdS-CdSO₄. The H⁺ to Cd²⁺ ratio has a maximum above which the purity decreases with increasing [H⁺]. Besides HCl and H²SO⁴, precipitations has also been done successfully with KCN and NH₄Cl [5].

Cd²⁺(aq) + H₂S(aq) CdS(s) [yellow]

In ammonia and cyanide under alkaline conditions, Cd²⁺ is easily precipitated by S²⁻:

[Cd(NH₃)₄]²⁺(aq) + S²⁻(aq) CdS(s) [yellow] + 4 NH₃(aq)
[Cd(CN)₄]²⁻(aq) + S²⁻(aq) CdS(s) [yellow] + 4 CN⁻(aq)

Reaction of cadmium with sulfur

In gaseous form, Cd and S₈ reacts forming CdS. At 130-180 °C solid Cd and S₈ reacts explosively, also forming CdS [5].

Cd(g) + S₈(g) CdS(g)
Cd(s) + S₈(s) CdS(s) [yellow]

Reaction of cadmium with sulfuric acid

Cadmium metal dissolves slowly in dilute sulphuric acid to form Cd(II) ion and hydrogen, H₂. In aqueous solution, Cd(II) is present as the complex ion [Cd(H₂O)₆]²⁺.

Cd(s) + H₂SO₄(aq) Cd²⁺(aq) + SO₄²⁻(aq) + H₂(g)

Reaction of cadmium with tellurium

Cd reacts rigorously with Te forming CdTe [5].

Cd(s) + Te(s)

~ 700 °C

CdTe(s)

Reaction of cadmium with water

Cadmium reacts with H₂O(g) forming H₂(g) at temperatures above 400 °C [5].

Cd(s) + H₂O(g) CdO(s) [Reddish-brown]

Cd only reacts very slowly with destilled water (24-48 h for reaction) [5].

Quantitative analysis